Recently, there has been provided a network which assures a quality of service (QoS) of a communication band or the like with introducing a concept of session (hereinafter, referred to as session control network) on an Internet protocol (IP) network which is based on the best-effort. Each terminal needs to support a protocol for session control in order to connect the terminal to such a session control network and benefit from the session control. However, the existing terminals are not compatible with the session control protocol in some cases.
Accordingly, there has been suggested a method in which a gateway unit substitutively performs session control processing between an existing terminal and a session control network, where the gateway unit is present between the existing terminal incompatible with a session control protocol and the session control network (for example, see Patent Literature 1 mentioned below).
On the other hand, in the case of the gateway unit substitutively performing the session control processing, the gateway unit needs to determine band information to be reported to the session control network for communication to be performed at the time of session control. Accordingly, for example, in the technique disclosed in Patent Literature 1 mentioned below, the gateway unit beforehand stores a correspondence table which correlates flow information with band information, the flow information being identified based on a sender address, a destination address, a protocol, a sender port number, a destination port number and the like in communications between the existing terminals, the band information being to be reported in session control. Then, the gateway unit looks up the correspondence table when having detected communication to be subjected to substitutive processing of session control, and retrieves the band information corresponding to the flow information of that communication, thereby to determine the band information to be reported to the session control network.